Jawaharlal Nehru Technological University Kakinada 2007 B.Tech Electrical and Electronics Engineering PULSE AND DIGITAL CIRCUITS (1) - Question Paper

Code No: R059210202 Set No. 4
II B.Tech I Semester Regular Examinations, November 2007
PULSE AND DIGITAL CIRCUITS
( Common to Electrical & Electronic Engineering, Electronics &
Communication Engineering, Electronics & Instrumentation Engineering
and Electronics & Telematics)
Time: three hours Max Marks: 80
ans any 5 ques.
All ques. carry equal marks
? ? ? ? ?
1. (a) What is the function of a comparator? discuss its operation.
(b) discuss the response of a low pass circuit to an exponential input is applied.
(c) discuss the response of RL circuit when a rectangular pulse is applied [4+6+6]
2. (a) For the circuit shown in figure 2a , Vi is a sinusoidal voltage of peak 100
volts. presume ideal diodes. Sketch 1 cycle of output voltage. Determine
the maximum diode Current.
Figure 2a
(b) discuss positive peak clipping with reference voltage. [12+4]
3. Write Short notes on:
(a) Diode switching times
(b) Switching characteristics of transistors
(c) FET as a switch. [4+8+4]
4. In the monostable circuit of the provided figure four the resistor R is connected to
an auxiliary supply V1 instead of VY Y . If A2 is in saturation or clamp and
if A1 is OFF in the stable state, verify that the gate time T is provided by Eq.
T =t ln(VYY+I1RY-Vs)/(VYY-V?) with VY Y changed by V1. [16]
1 of 3
Figure 4
5. (a) How are linearly varying current waveforms generated?
(b) In the boot strap circuit shown in figure5 Vcc = 25 V, VEE = -15 V, R = 10 K
ohms, RB = 150 K ohms, C = 0.05 µF. The gating waveform has a duration
of 300 µs. The transistor parameters are hie = 1.1Kohms, hre = 2.5 x 10-4 K
ohmshfe =50 hoe = 1/40K ohms.
i. Draw the waveform of IC1 and Vo , labeling all current and voltage levels,
ii. What is the slope fault of the sweep?
iii. What is the sweep speed and the maximum value of the sweep voltage?
iv. What is the retrace time Tr for C to discharge completely?
v. compute the recovery time T1 for C1 to recharge completely. [6+10]
Figure 5
2 of 3
6. (a) discuss how monostable multivibrator is used as frequency divider?
(b) Draw and discuss the block diagram of frequency divider without phase jitter.
[8+8]
7. (a) Why are sampling gates called linear gates?
(b) elaborate the other names of a gate signal?
(c) Compare the unidirectional and bi-directional sampling gates. [6+4+6]
8. (a) elaborate the basic logic gates which perform almost all the operations in
Digital communication systems.
(b) provide a few applications of logic gates.
(c) describe a positive and negative logic systems.
(d) Draw a pulse train representing a 11010111 in a synchronous positive logic
digital system. [4+4+4+4]

Earning:   Approval pending.